The invention relates to the field of gas phase polymerization reactions. In particular, the invention is directed to novel solid supported gas phase anionic polymerization catalysts for the production of diene elastomers, especially styrene butadiene rubber (SBR).
Gas phase fluidized bed, stirred or paddle-type reactor processes for the production of polymers, such as poly-xcex1-olefins and polybutadiene having highly desirable and improved properties, are well known. These gas phase processes, especially the gas fluidized bed process, provide a means for producing polymers with a drastic reduction in capital investment expense and a dramatic savings in energy usage and operating costs, as well as a greater margin of safety and fewer environmental concerns, compared to other conventional polymerization processes. The polymer products of gas phase polymerization processes are free-flowing granular powders that are readily compounded to form rubber products.
As in solution polymerization processes, a catalyst is usually required for polymerization of monomers in gas phase polymerization. However, the catalysts employed in gas phase polymerization of xcex1-olefins such as ethylene or propylene, or conjugated dienes such as butadiene, have hitherto been limited to solid supported Ziegler-Natta type catalysts based on titanium, vanadium and the like, solid supported chromium salts, Group VIII transition metal compounds, or other solid supported or solution transition metal coordination catalysts, and the like. Catalysts that exhibit activity in solution phase anionic polymerization reactions and those which operate by ionic or free radical mechanisms are typically not suitable for gas phase polymerization processes. Thus, none of the catalysts conventionally used in gas phase polymerization is capable of anionically copolymerizing conjugated dienes to form diene rubbers, which are the key raw materials used in the production of rubber tires.
Moreover, one of the disadvantages associated with supported gas phase catalysts is that the support material such as alumina, silica, and the like, remains behind in the polymer product as inorganic residual ash thereby increasing the overall impurity level of the polymer. Depending on the amount of such impurity, some of the properties of the polymers may possibly be affected, such as film appearance rating, impact resistance, tear strength, and the like. Another disadvantage of known gas phase polymerization processes using these catalysts is that they typically require undesirably large quantities (e.g., 30% in the product) of powdering filler materials, such as carbon black, in order to reduce the xe2x80x9cstickinessxe2x80x9d of the resulting polymer and prevent the agglomeration of the resin particles and the formation of large polymer chunks.
Because of the advantages of gas phase polymerization compared with solution polymerization, however, it would be useful to provide a gas phase anionic polymerization process by which diene elastomers, such as styrene butadiene rubber, polybutadiene rubber, polyisoprene rubber, and the like, can be economically and efficiently produced.
The invention provides solid supported anionic catalysts, suitable for gas phase anionic polymerization of conjugated diene monomers, that are useful for anionically producing very high molecular weight branched diene polymers, such as styrene butadiene rubber, polybutadiene rubber, polyisoprene rubber, and the like. Because of their extremely high molecular weight and controlled molecular weight distribution, glass transition temperature (Tg) and vinyl content, the macro-branched polymers produced by a gas phase anionic polymerization process employing the invention catalysts are useful for producing many different high performance vulcanates. The polymers synthesized by the process of the invention also exhibit other desirable properties, such as the ability to readily absorb hydrocarbon solvents and oils, and they are easily compounded to form vulcanizable elastomeric compounds and articles that have excellent resistance to wear and tear and exhibit reduced hysteresis properties.
In one embodiment of the invention, the catalyst has the formula P(Me)n, where P is a metalatable particle having a diameter of about 1 micron to about 1000 microns comprising a bound rubber. The particle is multiply-metalated with xe2x80x9cnxe2x80x9d covalently bonded Group IA alkali metal (Me) atoms. As used in the context of the invention and as known to one skilled in the art, the term xe2x80x9cbound rubberxe2x80x9d means rubber to which carbon black is attached by more than just physical entrainment and forms a simple carbon network with the rubber. The bound rubber particle may comprise any metalatable carbon black-bound rubber, such as carbon black-styrene butadiene rubber, carbon black-butadiene rubber, carbon black-natural rubber, and the like. As used in the context of the invention, the term xe2x80x9cmetalatedxe2x80x9d refers to an acid:base reaction, known to those skilled in the art, involving the transfer of a metal atom from a strong base to a more acidic polymer with the concomitant transfer of a hydrogen atom from the polymer to the base, thus forming a polymer carbon-metal atom covalent bond. A xe2x80x9cmetalatablexe2x80x9d bound rubber (or a metalatable thermoplastic polymer or a metalatable cured elastomer employed in embodiments of the invention) is one that can participate in this reaction and become metalated.
The number of metal atoms bound to the bound rubber particle ranges from n=3 to n=a multiplicity of atoms, 10X(e.g., 1010). The alkali metal atoms bonded to a single particle may all be the same or may be different from each other. The metal atoms may be any Group IA metal including lithium, sodium, potassium, rubidium, cesium and francium. Preferably the metal atoms are selected from lithium, sodium and potassium and, more preferably, are a mixture of lithium atoms and at least one of sodium atoms and potassium atoms. Most preferably, all of the alkali metal atoms are the same and are lithium atoms.
Other solid supported anionic catalysts that are suitable for use in gas phase polymerization of conjugated diene monomers, as described herein, are disclosed in U.S. Pat. No. 6,136,914, the disclosure of which relating to the initiators and methods for their preparation is hereby incorporated by reference. The disclosed initiators, which are also useful for solution phase anionic polymerization of conjugated diene monomers, have the same formula as the catalysts of the present invention but differ from the invention catalysts in that the particle portion of the disclosed initiators comprises a metalatable thermoplastic polymer (preferably having a Tg of 80xc2x0 C. to about 300xc2x0 C.) or a cured elastomer, rather than a bound rubber.
Each of the above previously disclosed anionic polymerization initiators and the invention anionic polymerization catalyst, when charged into the reaction zone of a gas phase polymerization apparatus, is capable of anionically homopolymerizing conjugated diolefin monomers having about 4 to about 12 carbon atoms and copolymerizing conjugated diolefin monomers and monovinyl aromatic monomers having from about 8 to about 20 carbon atoms to form very high molecular weight branched diene polymers.
The macro-branched diene polymers produced by the process of the invention are light, granular, and resemble a fish xe2x80x9ccaviarxe2x80x9d. In contrast to polymers produced by previous gas phase polymerization processes, the polymers produced by the above previously disclosed initiators and the invention catalyst are not sticky and do not produce agglomerates. Thus, the addition of diluting powdering agents is not required, resulting in a purer polymer product. Moreover, because the particles remaining behind in the polymer are polymeric, they do not add inorganic impurities to the resulting rubber product, and they are sheared (or dispersed) during compounding or milling, and processed like normal rubber.
The present invention provides the macro-branched diene polymers containing particles derived from the catalysts, a vulcanizable elastomer composition formed from the polymer, and a tire having at least one component formed from the vulcanizable elastomer composition. The invention further provides a method for preparing the solid supported anionic polymerization catalysts, and a method for gas phase anionic polymerization employing the invention catalysts and the initiators disclosed in U.S. Pat. No. 6,136,914, incorporated by reference above.
In another embodiment of the invention, an anionic gas phase polymerization method for producing high molecular weight diene polymers is provided in which ground particles such as graphitized carbon black, polyethylene, acetone-extracted scrap rubber, or the like are coated with oil in which free n-butyl lithium has been dissolved. A well known catalyst for anionic polymerization of linear polymers in solution is n-butyl lithium. It has been herein surprisingly discovered that a multiplicity of molecules of n-butyl lithium thus absorbed on the solid support particles also acts as a catalyst for gas phase anionic polymerization and, when charged into the reaction zone of a gas phase polymerization apparatus, is capable of anionically homopolymerizing conjugated diolefin monomers having about 4 to about 12 carbon atoms and copolymerizing conjugated diolefin monomers with monovinyl aromatic monomers having from about 8 to about 20 carbon atoms to form high molecular weight diene polymers.